158 PHOSPHORESCENCE. LECT. VIII. . 



If thirty or forty minutes intervened, before the introduc- 

 tion of the air or oxygen, the insects neither returned to 

 life nor re-acquired their phosphorescent quality ; the seg- 

 ments alone, having remained much longer in the carbonic 

 acid without being luminous, re-acquired their phosphores- 

 cence when oxygen was introduced. 



Effect of Hydrogen. When we used hydrogen, in place 

 of carbonic acid, the insects, as well as their separated lu- 

 minous parts, preserved their phosphorescence only for a 

 time, which was somewhat longer than that stated for car- 

 bonic acid. The difference was scarcely perceptible with 

 entire insects ; but was more considerable with the de- 

 tached luminous segments. In one instance, I saw the 

 phophorescence continue in hydrogen for twenty- five or 

 thirty minutes. And even insects that did not glow, in 

 hydrogen, returned to life and instantly re-acquired their 

 phosphorescence when they were exposed to the air, or, 

 better still, to oxygen gas ; provided that not more than 

 five or ten minutes had elapsed after the cessation of the 

 light. 



I invariably observed that, with the entire insects, the 

 intermittance ceased before the light had altogether disap- 

 peared. 



Some hours after the glow-worms, or their luminous 

 segments, had ceased to shine, a feeble but very visible 

 light was obtained by crushing them on the hand, but it 

 was only momentary. 



Effect of Atmospheric Mr. I now proceed to give you 

 an account of the most conclusive experiments which I 

 made whilst investigating the action of the insects, or their 

 luminous segments only, on atmospheric air, and on oxy- 

 gen. I placed in a small graduated bell-glass nine living 

 glow-worms, and in another similar vessel, containing as 

 much air, an equal number of detached segments. In 



